1. Field of the Invention
The present invention relates to sheet guiding means used for guiding transportation of a sheet material in, for example, a printer, a copying machine, or a facsimile, and an image forming apparatus including the same.
2. Description of the Related Art
A structure of a laser beam printer is schematically shown in FIG. 5 as a structure of a related image forming apparatus.
In the laser beam printer (image forming apparatus) shown in FIG. 5, when a sheet material S passes through a transfer nip section between a photosensitive drum 26A and a transfer roller 27, a toner image which has been formed on the photosensitive drum 26A by image formation processes, such as a charging operation, an exposure operation, and a developing operation, is transferred onto the sheet material S. Sheet material S, which may be paper, has been fed from a sheet-feed cassette 28, disposed at the bottom portion of the body of the image forming apparatus. After the toner image has been transferred onto the sheet material S, the toner image is fixed to the surface of the sheet material S by a fixing device 34. Here, when a one-side image formation mode is selected by an input operation from an operation panel (not shown), the sheet material S onto which the toner image has been transferred is discharged onto a sheet-discharge tray 37, disposed at the top portion of the image forming apparatus, thereby completing the formation of the image on one side of the sheet material S.
On the other hand, when a duplex image formation mode is selected, after the toner image has been fixed to one surface (a first surface) of the sheet material S, the sheet material S is not discharged onto the sheet-discharge tray 37, disposed above the sheet material S, but, is, instead, transported to a sheet re-feed path 52, disposed below the sheet material S.
The sheet material S which has been transported to the sheet re-feed path 52 is obliquely transported into a re-transportation path 59 by a transporting roller 50a and a diagonal-feed roller 50b. At this time, by bringing one of the edges (in the horizontal direction) of the sheet material S into contact with an oblique-movement correcting guide (not shown), oblique movement of the sheet material S in the horizontal direction is corrected. An electromagnetic shield plate 62 is disposed above the re-transportation path 59 and between the re-transportation path 59 and an electrical member 24. The bottom surface of the electromagnetic shield plate 62 restricts the position of the top portion of the sheet material S that is moving in the re-transportation path 59. A guiding member 51 is fixed to the downstream-side portion of the electromagnetic shield plate 62. The guiding member 51 forms what is called a restrictor portion which protrudes into the re-transportation path 59 in order to limit, from the vertical direction, the directional position of the re-transportation path 59.
The sheet material S is supplied to a downstream-side sheet re-feed roller 54 as a result of passing through the re-transportation path 59. The oblique movement of the supplied sheet material S is corrected by the oblique-movement correcting guide. In addition, for example, even when the supplied sheet material S is curled upward after the fixing operation, the front edge of the supplied sheet material S is smoothly guided to a nip section at the sheet re-feed roller 54 by the guiding member 51.
Of the labeled component parts in FIG. 5, those that are not described are similar to corresponding component parts shown in FIG. 1, which illustrates a first embodiment (described later). Therefore, they will be described later with reference to FIG. 1.
The electromagnetic shield plate 62, shown in FIG. 5, is, in general, formed of metal. Conventionally, the guiding member 51 has been a synthetic resin member secured to the electromagnetic shield plate 62.
Separately forming the guiding member 51 and the electromagnetic shield plate 62 results in additional costs of component parts and creation of manhours for performing mounting, which are, undoubtedly, disadvantageous from the viewpoint of costs. In addition, a parts gap 57 may be formed between the electromagnetic shield plate 62 and the guiding member 51 due to, for example, variations in the dimensions of the parts. This may result in the front edge of the sheet material S getting stuck and, thus, jammed in the parts gap 57.
In particular, when the guiding member 51 is a resin member, it tends to wear and to get scraped when an edge of the sheet material S collides therewith, so that the sheet material S catches in the worn and scraped portion of the guiding member 51. Therefore, due to this reason also, jamming tends to occur. Further, since the sheet material S rubs against the guiding member 51, triboelectricity tends to occur. This may prevent smooth transportation of the sheet material S.
Although, in the foregoing description, the problems of increased costs, jamming, and improper transportation of the sheet material S are described as occurring in the re-transportation path, these problems may also occur in other commonly provided transportation paths.
In view of the above-described circumstances, it is an object of the present invention to provide sheet guiding means which makes it possible to prevent increased costs and improper transportation, including jamming, of sheets, and to provide an image forming apparatus including such sheet guiding means.
To this end, according to one aspect of the present invention, there is provided a sheet guiding device for guiding a sheet material. The sheet guiding device comprises an electromagnetic shield plate which is disposed between an electrical member and a sheet transportation path. In the sheet guiding device, by disposing the electromagnetic shield plate along the sheet transportation path, a sheet-transportation-path-side surface of the electromagnetic shield plate is used as a sheet guiding surface for guiding the sheet material through a guiding section. In addition, in the sheet guiding device, a portion of the electromagnetic shield plate protrudes into the sheet transportation path in order to form the protruding portion of the electromagnetic shield plate and thereby narrow the sheet transportation path in a vertical direction.
According to one aspect of the present invention, the electromagnetic shield plate is disposed at a sheet re-feed path for the sheet material, and the sheet material which is re-fed is guided by the guiding section.
In accordance with this aspect, the electromagnetic shield plate may be disposed above the sheet transportation path so that the sheet guiding surface restricts the sheet material which is transported in the sheet transportation path, from above the sheet material.
In accordance with another aspect of the invention, the sheet guiding device further comprises an oblique movement correcting guide which corrects an oblique movement of the sheet material by coming into contact with one of the edges, in a horizontal direction, of the sheet material which is being transported, wherein a guide length of the guide section and a guide length of the oblique movement correcting guide are set substantially equal to each other.
In accordance with this aspect of the invention, a height of the bottommost portion of the guide section and a height of the topmost portion of the oblique movement correcting guide are set substantially equal to each other.
According to still another aspect of the present invention, there is provided an image forming apparatus comprising an image forming section which forms an image on a surface of a sheet material which has been supplied, and a sheet transportation path used to guide the sheet material when the sheet material is supplied to the image forming section and after the image has been formed on the sheet material. In the image forming apparatus, the sheet guiding device of any one of the one aspect to the fourth form of the one aspect is provided at a portion of the sheet transportation path.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.